1. Field of the Invention
The invention relates to techniques for manufacturing resin based products and more particularly relates to resin products containing filler having a relatively low specific gravity, which resin products are useful to form plate- or sheet-like products that may be utilized in vehicles.
2. Description of Related Art
Japanese Laid-open Patent Publication No. 05-245962 discloses a general technique for continuously manufacturing a synthetic resin laminate plate using a synthetic resin mixed with a filler. This technique utilizes an extrusion formation method that employs a T die. The filler that is mixed into the synthetic resin in this known method may be an inorganic or organic substance. When talc, calcium carbonate, or a similar inorganic substance is used as the filler in such an extrusion formation method, the product quality is satisfactory, but the specific gravity (density) of the resulting material is relatively high. Therefore, the weight of products made from such resin materials is also relatively high. When sawdust or another such organic filler substance is used as the filler, the sawdust is finely pulverized or carbonized at the time of extrusion, and the specific gravity (density) of the resulting material consequently does not decrease. Therefore, the weight of products made from such resin materials does not decrease. In addition, moisture contained in the sawdust evaporates during the manufacturing process and results in a decreased product quality. Moreover, increasing the amount of sawdust added to the resin reduces the adherence of the melted resin. Therefore, it has always been difficult to continuously form useful resin products employing such extrusion techniques.
Techniques for continuously manufacturing a plate- or sheet-like formed product are also known in which a synthetic resin containing a resin material or rubber material is melted. In such techniques, the melted material is pressure joined and then cooled to produce a solid synthetic resin product. If a laminate product will be manufactured using, for example, a melted resin material and a coating material, the melted resin material is dropped directly onto the coating material, and then the melted resin material is covered with another coating material. The resin material is pressure joined on both sides to the coating materials and cooled to yield a synthetic resin product having a laminate construction. This method, however, is problematic in that temperature differences between the two surfaces of the resin material at the time that the coating materials are joined to the melted resin material result in differential contraction as well as warping and distortion at the time of cooling. The resin material may, for example, contract due to faster cooling on the surface of the side that is kept at a higher temperature during the pressure joining step.
It is, accordingly, one object of the present invention to teach effective techniques for producing a high quality resin product.
The resin formed product may, for example, be formed by laminating a surface resin layer onto an intermediate resin layer that comprises a resin. The intermediate resin layer preferably comprises a granular ground substance of plant origin. In addition, air is preferably incorporated into the interior of the melted resin, when it is melted by stirring using a stirring device such as a blade. Preferably, a ground plant product having a specific gravity (density) less than the specific gravity (density) of the resin is mixed into the intermediate resin layer in order to reduce specific gravity (density) of the intermediate resin layer. Thus, the weight of the resin product will be less than if the ground plant product was not utilized. If the intermediate resin layer has a porous quality, a further reduction in weight of the resin product is possible.
A foaming agent is preferably mixed into the melted resin that will become the intermediate resin layer in addition to the ground substance of plant origin. The gas released by the foaming agent increases the porous nature of the intermediate resin layer and results in further weight reduction.
Preferably, at least one of the surface resin layers includes at least one depression and preferably may include a plurality of depressions. A roller or similar pressing member that presses the surface resin layer onto the intermediate resin layer may be used when the surface resin layer and the intermediate resin layer are adhered to each other. The surface of the pressing member may include a protrusion and this protrusion may be used to form the depression(s) on the surface resin layer. The volume of the intermediate layer is thereby decreased in correspondence to the depression(s), which reduces the material costs associated with the resin laminate product and results in further weight reduction. Furthermore, the pressing member acts to press the surface resin layer and form the depression(s). Thus, the synthetic resin laminate product may be continuously manufactured with high production efficiency.
Kenaf is preferably used in the ground product of plant origin. Kenaf is an African or East Indian plant having a botanical name of Hibiscus cannabinus and is also known as ambary. Kenaf yields a useful fiber that is used in canvas and cordage and the fiber has a specific gravity of between about 0.1 and 0.2, as compared to water at 4xc2x0 C. (i.e. 1 gram per cubic centimeter). The use of kenaf has the benefit of preserving forest resources and thereby providing an environmentally friendly manufacturing process. Furthermore, waste resin materials may be utilized in the synthetic resin in order to recycle waste resin materials, which may increase the environmentally friendly manner of the manufacturing process.
If the resin formed product will be manufactured by pressure joining the melted resin on both sides by way of a contact surface, the temperature of the contact surface may be regulated or adjusted so that both surfaces of the melted resin are kept at the same or similar temperature. By keeping the temperature of both surfaces of the melted resin similar during pressure joining, the surfaces are prevented from contracting at different rates, thereby minimizing or preventing warping and distortion. If a pair of contact surfaces having similar heat conductance is used, the contact surfaces are maintained at an identical temperature and simultaneously contact the melted resin. Thus, the temperatures of both surfaces of the melted resin are kept similar during the pressure joining step.